How to read for X seconds maximum in C++?

Question

I want my program to wait for something to read in a FIFO, but if the read (I use std::fstream) lasts more than 5 seconds, I want it to exit.

Is it possible or do I have to use alarm absolutely?

Thank you.

Answer 1

I do not believe there is a clean way to accomplish this that is portable C++ only solution. Your best option is to use poll or select on *nix based systems and WaitForSingleObject or WaitForMultipleObjects on Windows.

You can do this transparently by creating a proxy streambuffer class that forwards calls to a real streambuffer object. This will allow you to call the appropriate wait function before doing the actual read. It might look something like this...

class MyStreamBuffer : public std::basic_streambuf<char>
{
public:
    MyStreamBuffer(std::fstream& streamBuffer, int timeoutValue)
        : timeoutValue_(timeoutvalue),
          streamBuffer_(streamBuffer)
    {
    }

protected:
    virtual std::streamsize xsgetn( char_type* s, std::streamsize count )
    {
        if(!wait(timeoutValue_))
        {
            return 0;
        }

        return streamBuffer_.xsgetn(s, count);
     }

private:
     bool wait() const
     {
         // Not entirely complete but you get the idea
         return (WAIT_OBJECT_0 == WaitForSingleObject(...));
     }

    const int       timeoutValue_;
    std::fstream&   streamBuffer_;
};

You would need to do this on every call through. It might get a little tedious but would provide a transparent solution for providing timeouts even where they might not be explicitly supported in client code.